Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D213/00—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members
  • C07D213/02—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members
  • C07D213/04—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members having no bond between the ring nitrogen atom and a non-ring member or having only hydrogen or carbon atoms directly attached to the ring nitrogen atom
  • C07D213/24—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members having no bond between the ring nitrogen atom and a non-ring member or having only hydrogen or carbon atoms directly attached to the ring nitrogen atom with substituted hydrocarbon radicals attached to ring carbon atoms
  • C07D213/28—Radicals substituted by singly-bound oxygen or sulphur atoms
  • C07D213/30—Oxygen atoms

Definitions

• Hydroxymethylpyridines are valuable intermediates and find use, for example, in the synthesis of pharmaceuticals and agrochemicals, such as mefloquine hydrochloride or pineprofen.
• a further possibility is the catalytic reduction of pyridinealdehydes using H 2 over Ba-promoted Cu chromite catalysts at 180 to 230° C. according to Chem. Abstr. Vol. 103: 215198 or the reduction with NaBH 4 according to Chem. Abstr. Vol. 93: 71487, and the latter says that the reactivity of the aldehydes toward reduction decreases in the order 2,6-pyridinecarboxaldehyde, 6-methyl-2-pyridinecarboxaldehyde, 4-pyridinecarboxaldehyde, 2-pyridinecarboxaldehyde and 3-pyridinecarboxaldehyde.
• a further disadvantage is the poor availability of the pyridinealdehyde.
• Examples of other known variants are electro-chemical reduction of picolinic esters (e.g.: EP-A1-0 189 678) or the oxidation of alpha-picoline N-oxides sing trifluoroacetic anhydride (e.g.: Chem. Abstr. Vol. 122: 239462).
• the invention accordingly provides a process for preparing hydroxymethylpyridines which comprises
• the process of the invention provides hydroxymethylpyridines (HMPs) in high purity.
• the process is particularly suitable for preparing a multiplicity of hydroxymethylpyridines such as 2-, 3- or 4-hydroxymethylpyridine, 6-methyl-2-hydroxy-methylpyridine, 2,6-di(hydroxymethyl)pyridine, etc.
• 2-, 3- or 4-hydroxy-methylpyridine are preferably prepared, and 2-hydroxymethylpyridine is more preferably prepared.
• the corresponding vinylpyridine serves as the starting compound, such as 2-, 3- or 4-vinylpyridine, 6-methyl-2-vinylpyridine and 2,6-divinylpyridine, which is converted in the first step by ozonolysis with subsequent catalytic hydrogenation.
• the ozonolysis is carried out at temperatures of ⁇ 80° C. to +20° C., preferably at ⁇ 30° C. to +10° C. and more preferably at ⁇ 25° C. to +5° C.
• the reaction with ozone takes place in an aliphatic C 1 -C 4 -alcohol, such as methanol, ethanol, butanol or propanol.
• an aliphatic C 1 -C 4 -alcohol such as methanol, ethanol, butanol or propanol.
• Preferred solvents are methanol and ethanol, of which methanol is more preferred.
• the catalytic hydrogenation of the ozonolysis products following the ozonization preferably takes place in highly dilute solution, the measure described below ensuring that during the entire hydrogenation a peroxide content of maximum 0.1 mol/l, preferably of maximum 0.05 mol/l and in particular of maximum 0.02 mol/l is set and maintained.
• a hydrogenation reactor is charged with a suspension of the catalyst in the alcoholic solvent used during ozonolysis and the solution resulting from the ozonization is continuously fed in by means of an adjustable metering apparatus. While the ozonization solution is added at the beginning and in the course of the hydrogenation care must of course be taken that the peroxide content in the hydrogenation reactor specified above not be exceeded owing to the introduced amount of the peroxidic ozonolysis products.
• the continuous addition moreover allows a large quantity of ozonolysis products to be reduced in a comparatively small volume, which results in high concentrations of the corresponding HMP and savings in time and also in the costs of the distillative removal of the solvent.
• Useful catalysts for the hydrogenations are suitable noble metal catalysts, which may be used in the form of powder catalysts with support materials or without support material. Palladium or platinum catalysts are preferably used. Examples of suitable support materials for powder catalysts include carbon, aluminum, silica gel or kieselguhr. Although yields are independent of the catalyst quantity used, in order to attain a sufficient hydrogenation rate it is recommended to use an initial charge of the catalysts mentioned in noble metal quantities of from 0.1 to 20% by weight, preferably from 1 to 15% by weight and more preferably from 5 to 10% by weight, based in each case on the total quantity of the ozonized vinylpyridines fed in per hour.
• the catalyst is separated from the reaction mixture.
• equivalent quantities of hydrogen are consumed in reducing the ozonolysis products.
• the quantity of hydrogen which can be used in the hydrogenation ranges from one mole equivalent to a multiple molar excess. From 1.3 to 2.5 mol equivalents of hydrogen are preferably used, and from 1.8 to 2.2 mol equivalents are more preferably used.
• the hydrogenation advantageously takes place under virtually atmospheric conditions.
• Virtually atmospheric conditions are to be understood as meaning pressures of from 1 to about 3 bar, as is customary in industrial practice to prevent ingress of air into the hydrogenation reactor.
• the reduction of the ozonolysis products is very simple to practice in industry.
• the reduction is exothermic and in a preferred embodiment is conducted at temperatures of from 20 to 60° C., in particular at temperatures in the range from 35 to 50° C.
• the reaction solution is separated from the catalyst and preferably concentrated, for example using a rotary evaporator, and the alcohol used as solvent is distilled off as an alcohol-water mixture.
• the formaldehyde formed as a by-product of the conversion of the vinylpyridines to the corresponding HMP is also removed substantially from the reaction solution.
• formaldehyde can be converted, for example by means of an acidic ion exchanger to formaldehyde dialkyl acetal, separated distillatively from the alcohol and then burnt.
• the remaining reaction solution is then admixed with a suitable base, such as NaOH, KOH, CaOH, etc., and preferably with NaOH in combination with aqueous ammonia, preferably in 25% strength, so that a pH value of from 10 to 14, preferably from 11 to 13 is set.
• a suitable base such as NaOH, KOH, CaOH, etc.
• reaction solution remaining after the concentration can also be admixed only with one suitable base, such as NaOH, KOH, CaOH, etc., preferably 20 to 50% strength NaOH without aqueous ammonia, again until a pH of from 10 to 14, preferably from 11 to 13, is attained, and heated to from 60 to 110° C., preferably from 75 to 85° C.
• one suitable base such as NaOH, KOH, CaOH, etc.
• NaOH sodium hydroxyanisole
• KOH potassium hydroxyanisole
• CaOH aqueous ammonia
• the reaction solution remaining after the concentration can also be admixed only with one suitable base, such as NaOH, KOH, CaOH, etc., preferably 20 to 50% strength NaOH without aqueous ammonia, again until a pH of from 10 to 14, preferably from 11 to 13, is attained, and heated to from 60 to 110° C., preferably from 75 to 85° C.
• the by-produced alkyl picolinate is again hydrolyzed and the remaining formal
• the hydrogenation solution can be sucked into a basic initial charge, such as an NaOH, KOH or CaOH initial charge, preferably into a 20 to 50% strength NaOH initial charge, using a rotary evaporator, and alcohol and water are simultaneously distilled off, which again results in the hydrolysis of the by-produced alkyl picolinate and the conversion of the remaining formaldehyde into formate and methanol, but scarcely any formaldehyde can be detected in the distillate.
• the pH here is also from 10 to 14.
• extraction is performed using an organic solvent at a temperature of from 15 to 50° C., preferably from 20 to 45° C.
• Suitable solvents include customary extractants that are inert under the reaction conditions, such as toluene, ether, etc.
• Ethers are preferably used, more preferably methyl t-butyl ether (MTBE).
• MTBE methyl t-butyl ether
• the collected organic phases are then concentrated and the residue is distilled at from 10 to 200 mbar, preferably at from 30 to 100 mbar, more preferably at from 40 to 60 mbar, and at the maximum necessary liquid phase temperature.
• about 5% is preferably separated off as the first cut and about 5% as the bottom product.
• An advantage of the work-up of the invention is that in particular in the preferred embodiment no formaldehyde has to be burnt and in the event of any incomplete hydrogenation the corresponding pyridinealdehyde formed by the ozonolysis is converted to a substantial extent (over 70%) by the formaldehyde present in excess by a crossed Cannizzaro reaction to the corresponding hydroxymethylpyridine.
• a further advantage is that the by-products resulting from the ozonolysis-reduction mechanism, such as pyridine-carboxylic acid, pyridine-carboxylic esters, pyridinealdehyde and formaldehyde can be easily removed and the end products can be obtained in yields of up to 80% and a purity of above 99.5% by weight.
• a 0.5 mol solution of 2-vinylpyridine in methanol was ozoninized at ⁇ 15° C. using ozone in a concentration of 50 g/m 3 h and the solution obtained in this way fed via a feed vessel into a hydrogenation reactor, which had been initially charged with a suspension of 5% Pd/C catalyst in methanol and filled with hydrogen, at such a rate that the peroxide content did not exceed 0.02 mol/l.
• Hydrogenation was continued with vigorous stirring and hydrogen addition until a negative peroxide test was obtained, and the temperature was held at 45° C. After the hydrogenation had ended, the catalyst was separated off.
• the hydrogenation solution obtained in this way was continuously sucked into an initial 40% sodium hydroxide charge with a pH value above 12 and methanol/water was simultaneously distilled off at 80° C. and under slightly reduced pressure. During this 3.5-hour process, the methyl picolinate was hydrolyzed and the formaldehyde converted to sodium formate and methanol. Almost no formaldehyde could be detected in the distillate by oxime titration (less than 50 mg/l of methanol).
• the collected organic phases were concentrated on a rotary evaporator at 60° C. and under slightly reduced pressure and the residue distilled at a maximum of the necessary liquid phase temperature of 140° C. and 50 mbar. During the distillation, about 5%, which comprised ethylpyridine, water, etc., was separated off as first cut and 5% as bottom product.
• the purity of the colorless main fraction was >99% and the formaldehyde content ⁇ 100 ppm.
• the yield of 2-hydroxymethylpyridine was 67% based on the 2-vinylpyridine used.
• the hydrogenation solution obtained in this way was continuously sucked into a rotary evaporator and methanol/water/formaldehyde were simultaneously distilled off at 80° C. and under slightly reduced pressure. During this 3.5-hour process, 90% of the formaldehyde was distilled off.
• Methyl picolinate was then hydrolyzed by addition of 40% sodium hydroxide in excess and the remaining formaldehyde converted to sodium formate and methanol at 80° C. within 2 hours.
• the collected organic phases were concentrated on a rotary evaporator at 60° C. and under slightly reduced pressure, and the residue distilled at a maximum of the necessary liquid phase temperature of 150° C. and 50 mbar. During the distillation, about 5%, which comprised ethylpyridine, water, etc., was separated off as first cut and 5% as bottom product.
• the purity of the colorless main fraction was >99% and the formaldehyde content ⁇ 100 ppm.
• the yield of 2-hydroxymethylpyridine was 76% based on the 2-vinylpyridine used.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Pyridine Compounds (AREA)
• Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)
• Hydrogenated Pyridines (AREA)

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• 1999
  • 1999-11-26 AT AT0200499A patent/AT408099B/de not_active IP Right Cessation
• 2000
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